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Power - Pentode (NOT beam) ·Pentode

1AC5

Ultra-low-power directly heated pentode for battery audio-output service from plate supplies as low as 45–67.5 V.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
8CP
Socket code
IO
Base pins
8
Nominal heater
1.25 V / 40 mA

Description

1AC5 — Subminiature Power Amplifier Pentode

The 1AC5 is a subminiature power amplifier pentode designed for low-power applications. It features a directly heated filamentary cathode designed for efficient DC operation, making it suitable for compact, battery-operated equipment where power consumption must be minimized.

Construction, Filament, and Base Configuration

The 1AC5 is constructed in a subminiature envelope, designated by outline drawing 3-5. It utilizes a directly heated filament cathode that operates on a nominal DC supply.

Filament ParameterValue
Filament Voltage (DC)1.25 V
Filament Current0.04 A (40 mA)
Calculated Filament Power0.05 W (50 mW)

The calculated filament power is derived from the nominal ratings: Power=1.25 V×0.04 A=0.05 W\text{Power} = 1.25\text{ V} \times 0.04\text{ A} = 0.05\text{ W}

The tube features an 8CP base connection. The pin assignments, viewed from the bottom of the base, are as follows:

Pin NumberElectrode Connection
Pin 1Filament Negative (F-)
Pin 2Grid No. 1 (G1)
Pin 3Grid No. 2 (G2)
Pin 5Plate (P)
Pin 8Filament Positive (F+)

Maximum Ratings

The maximum ratings for the 1AC5 are established under the Absolute Maximum System. Operating the device beyond these limits may impair its performance or longevity.

ParameterAbsolute Maximum Rating
Plate Voltage67.5 V max
Screen Voltage (Grid No. 2)67.5 V max

Typical Operation and Electrical Characteristics

The 1AC5 is designed to operate as a Class A amplifier. The electrical characteristics and performance vary depending on the chosen operating voltage. Three typical operating conditions are documented, demonstrating the tube's performance at plate and screen potentials ranging from 30 V to 67.5 V.

ParameterOperating Condition 1Operating Condition 2Operating Condition 3
Plate Voltage67.5 V45 V30 V
Screen Voltage67.5 V45 V30 V
Negative Grid Voltage4.5 V3.0 V2.0 V
Plate Current2.0 mA1.0 mA0.5 mA
Screen Current0.4 mA0.2 mA0.1 mA
Plate Resistance (RpR_p)~150,000 Ω~170,000 Ω~200,000 Ω
Transconductance (GmG_m)750 µmhos600 µmhos450 µmhos
Load Resistance25,000 Ω40,000 Ω50,000 Ω
Power Output0.050 W (50 mW)0.015 W (15 mW)0.005 W (5 mW)

As the operating voltages are reduced, the plate resistance increases from approximately 150,000 Ohms to 200,000 Ohms, while the transconductance decreases from 750 µmhos to 450 µmhos. This shift requires a higher load resistance (up to 50,000 Ohms at 30 V) and results in a lower power output, dropping from 50 mW at the maximum typical operating point to 5 mW at the lowest typical operating point.

Technical Summary

The 1AC5 is a subminiature, directly heated power amplifier pentode. It operates with a highly efficient 1.25 V, 40 mA DC filament. Utilizing an 8CP base connection, it provides reliable Class A audio or power amplification at low plate and screen voltages up to an absolute maximum of 67.5 V. Depending on the operating point, it delivers between 5 mW and 50 mW of power output into loads ranging from 25,000 Ω to 50,000 Ω, making it an optimized choice for low-drain, low-voltage subminiature designs.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
8CP
Socket code
IO
Base pins
8
Nominal heater voltage
1.25 V
Nominal heater current
40 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

8CP - Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

1 physical section, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances
Plate resistance
150000 Ω
Transconductance
0.00075 S
Max plate voltage
67.5 V
Max screen voltage
67.5 V

Power amplifier pentode.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

195X General Electric Essential Characteristics

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • Plate voltage

    67.5 V

    ClassA

  • Screen voltage

    67.5 V

    ClassA

  • Grid voltage

    -4.5 V

    ClassA

  • Plate current

    2 mA

    ClassA

  • Screen current

    0.4 mA

    ClassA

  • Load resistance

    25000 ohm

    ClassA

  • Power output

    0.05 W

    ClassA

  • Plate voltage

    45 V

    ClassA

  • Screen voltage

    45 V

    ClassA

  • Grid voltage

    -3 V

    ClassA

  • Plate current

    1 mA

    ClassA

  • Screen current

    0.2 mA

    ClassA

  • Plate resistance

    170000 ohm

    ClassA

  • Transconductance

    600 uS

    ClassA

  • Load resistance

    40000 ohm

    ClassA

  • Power output

    0.015 W

    ClassA

  • Plate voltage

    30 V

    ClassA

  • Screen voltage

    30 V

    ClassA

  • Grid voltage

    -2 V

    ClassA

  • Plate current

    0.5 mA

    ClassA

  • Screen current

    0.1 mA

    ClassA

  • Plate resistance

    200000 ohm

    ClassA

  • Transconductance

    450 uS

    ClassA

  • Load resistance

    50000 ohm

    ClassA

  • Power output

    0.005 W

    ClassA